1. Technical Field
Embodiments of the invention relate to semiconductor devices having a stable output period of a data strobe signal and semiconductor systems including the same.
2. Related Art
Semiconductor memory devices have been continuously developed to improve the operation speed thereof with increase of their integration density. For example, synchronous memory devices operating in synchronization with external clock signals have been revealed to improve the operation speed thereof.
Single data rate (SDR) synchronous memory devices have been first proposed to enhance the operation speed of the semiconductor memory devices. The SDR synchronous memory devices receive or output the data in synchronization with every rising edge of an external clock signal.
However, high performance memory devices, which are faster than the SDR synchronous memory devices, are still required to meet the requirements of high performance electronic systems. Accordingly, double data rate (DDR) synchronous memory devices operating at a higher speed than SDR synchronous memory devices have been proposed recently. The DDR synchronous memory devices may receive or output the data twice during a single cycle time of an external clock signal. That is, the DDR synchronous memory devices may receive or output the data in synchronization with every rising edge and every falling edge of the external clock signal. Thus, the DDR synchronous memory devices may operate at a speed which is twice higher than that of the SDR synchronous memory devices even without increase of a frequency of the external clock signal.
In a semiconductor system, a data strobe signal may be used for data exchange between semiconductor devices in the semiconductor system or between a semiconductor device and a controller in the semiconductor system. The data strobe signal may be transmitted with data through a data transmission line. Thus, transmission of the data strobe signal and the data may be affected by a signal delay time of the data transmission line. Accordingly, if the data are inputted or outputted in synchronization with the data strobe signal, the data may be stably inputted to or outputted from the semiconductor system.